It will be the case in the future that new battery systems will increasingly be used both in stationary applications (for example in wind power installations) and in vehicles (for example in hybrid and electric vehicles), with very stringent requirements in terms of reliability being placed on these new battery systems. The background for these stringent requirements are that failure of the battery can result in failure of the entire system (for example failure of the traction battery in an electric vehicle) or even in safety-relevant problems (in wind power installations batteries are used, for example, for protecting the installation from impermissible operating states as a result of rotor blade adjustment in the case of a strong wind).
In order to enable isolation of the battery system from the connected consumers, for example from an on-board vehicle power supply system, relays (or contactors) are generally provided in series with the two battery terminals. These relays must make it possible for such a system to be disconnected a plurality of times on load. In order to meet these stringent requirements, it needs to be possible to both diagnose and predict the functionality of these relays.
In relays and contactors, a switchable electromagnet acts as drive for the actuation of contacts for switching on, switching off and switching over an electrical load. In this case, the contacts are in principle subject to different levels of wear during switching of electrical loads, and this wear increases considerably in the case of loads with medium to high powers. In this case, it may also arise that the contacts are welded to one another and thereby jam, which can result in considerable hazard situations. It is therefore necessary to monitor the state of the switching contacts and to introduce corresponding additional disconnection measures for the electrical load.
DE 20310043 U1 describes a monitoring apparatus in which a check element for the coil of the relay is associated with the relay to be monitored. The checking device in this case provides information in respect of whether the coil has been actuated or not. This is made possible by virtue of the fact that the check element comprises a component part which is sensitive to magnetic fields and is arranged in the vicinity of the coil in such a way that, when the coil is switched on, the magnetic field produced by said coil flows through said check element, as a result of which the magnetic field of the coil activates the check element. In this case, a reed contact is provided as check element. One disadvantage with such an arrangement consists in that an additional component part necessarily needs to be provided on the relay to be monitored.